Practice of Plant Breeding 



tion or hybridising, although it is perhaps infinitely 

 more difficult. Some results are very unexpected. 



Muller (Thurgau) selected ten potatoes of, as nearly 

 as possible, exactly equal size. Five were kept in an 

 ice-house and the others in a house cellar at ordinary 

 temperature. Both were planted at the same time, but 

 those from the ice-house gave a large crop three months 

 after planting, when those which had been kept warm 

 had only begun to sprout ! 



One unfortunate point about all man's selected and 

 improved varieties is that they are apparently doomed 

 sooner or later either to degenerate and fall back into 

 their original state, or to become so feeble in constitu- 

 tion that they readily fall a prey to fungus-diseases or 

 insect-attacks. 



Some practical plant-breeders doubt whether this 

 must necessarily happen. There is a long discussion of 

 the subject in the Journal of the Royal Horticultural Society 

 for December 1906, especially with regard to potato- 

 degeneration. Some excellent sorts, such as Victoria, 

 degenerate quickly, and others (Dunbar Regent) have 

 vanished, although they were heavy croppers and of 

 an excellent quality. The best types of 1845, such as 

 Buffs and Dons, are no longer to be found. 



There are, it is true, apparent exceptions, such as 

 Ashleaf and Early Rose, which seem to have perennial 

 youth ; but these are early varieties, which would pro- 

 bably escape the worst attacks of the fungus in any 

 case. 



Of course when a plant is propagated continually by 

 tubers, it is just the same individual plant that goes on 

 living from year to year, and one would expect it to 

 grow old and feeble. But 500 years is not a very 

 great age for some trees, which may live to 3000 years 

 or more under exceptional conditions. No variety of 



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